The present invention relates to a ring laser angular rate sensor, a so-called ring laser gyro. More particularly it relates to a readout apparatus for such a ring laser gyro.
A so-called ring laser gyroscope is basically a laser apparatus having a ring type resonant cavity, typically triangular in configuration. The laser beam is directed around the triangular path by suitable mirrors positioned at each of the corners of the triangular structure. In most cases there are two laser beams traveling in opposite directions relative to each other around the ring. The positioning of the mirrors in the corners of the ring, or triangle, direct the laser beams down the channels of the resonant cavity. At one of the corners, the mirror must take the form of a so-called beam splitter. There a portion of each of the laser beams is reflected into the resonating cavity while another portion of each of the beams is transmitted through the mirror into a readout assembly. Some examples of ring laser gyros are shown and described in U.S. Pat. Nos. 3,373,650; 3,390,606; 3,467,472; and 4,152,071, all of which are assigned to the assignee of the present application. The readout apparatus for such ring laser gyros, as noted in the aforementioned patents, have been in the form of either a single beam readout arrangement or in the form of a so-called double beam readout arrangement, each having its own unique characterics.
In a co-pending application Ser. No. 482,665, filed Apr. 6, 1983, now U.S. Pat. No. 4,582,429, in the name of Stephen Callaghan and assigned to the assignee of the present invention, there is disclosed a readout assembly which features both single and double beam type readouts. In that application, there is presented a symmetrical arrangement of two prismatic elements which are secured to each other at a common face by a suitable optical cement and both elements are similarly cemented to a substrate block. Although such stucture has provided significant improvements in the readout capabilities of the associated ring laser gyro, it has been found that the use of such cements or adhesives has lead to instabilities, stresses and warpage of parts. Additionally, the use of such adhesives has further involved long and tedious assembly requiring fine adjustments as the adhesives cure.